Hi there, thanks for replying. Yes, they did erase the "unknown" diagnostic code. And there has been no further incident of the "check engine" light coming back on.

However, I was just concerned that it was some kind code that only volvo dealerships could know and that would mean I would no choice but to take my car back to them.

I don't want to go back to the over priced dealership and imcompetent service department. You know , they say "replace" to everything without even looking at the part in question. I had a seat belt problem which the dealership automatically said replace at the tune of $250. I decided to take the problem to my currrent mechanics. They fixed it in less than 10 minutes without even charging me for labor. It was nothing more than a penny had fallen into the locking mechanism. Thought you might enjoy that story!